Digital communication systems frequently require quadrature modulation of complex baseband signals. Quadrature modulation usually involves multiplication with a complex exponential and subsequently extracting the real part of the complex product for transmission into the medium. The extraction of the real part might cause a negative frequency image to corrupt the main signal. This negative frequency image can be, for example, a sampling image caused by a prior upsampling step in the digital domain.
One way to reduce this problem is to have sufficient filtering of the image. But this is usually a costly approach.